Currently, as a research project of the 3rd Generation Partnership Project (3GPP), complete radio communication standards have been formed for the LTE, and are being promoted gradually in the world.
However, Circuit Switched (CS) domain services are not supported by LTE. Therefore, a terminal cannot directly establish a CS domain call in an LTE cell. If the terminal resides in the LTE cell and herein the terminal is called by a CS domain service, then the LTE system cannot process the call of the CS domain service, thus leading to a call failure.